Botulism killing Erie fish, birds
Thousands of Lake Erie fish and shorebirds are dying from a mysterious outbreak of type E botulism. The natural bacteria is found in the lake's sediment and normally forms in the carcasses of dead fish. Wildlife experts say there's little they can do.
Scientists are puzzled as to why the organism responsible for the toxin has found its way into live fish, and what worries them more is large numbers of loons will likely be the next to die from ingesting the toxin when they begin migrating south in October and stop at Lake Erie to feed.
Most of the dead fish, primarily sheepshead, and a variety of birds such as gulls, cormorants and terns, have been found on a stretch of Lake Erie east from Port Dover, said Jeff Robinson, Ontario wildlife area manager for Environment Canada, who is based in the Canadian wildlife service office in London.
US scientists on the south side of Lake Erie, which is also littered with dead fish, are trying to determine whether the toxin is being transmitted by a recent invader, the small round goby fish which now inhabits the lake after coming from the Caspian Sea in eastern Europe, as did the troublesome zebra mussel in the mid-1980s.
Dying sheepshead collected 2 weeks ago by the US Department of Environmental Conservation from the shore of Lake Erie near Buffalo were found to have botulism and to have fed on gobies.
The goby is one of the few lake invaders which feed on the zebra mussel at the bottom of the lake.
"We're not really sure what's going on," said Robinson. "But what seems to be the current thinking is the goby fish are part of the reason this botulism has come up through the food web."
John Cooper, a spokesman for the Lake Erie management unit of the Ontario Ministry of Natural Resources, said it is common for fish to die in Lake Erie and wash up on shore during the summer as a result of thermal inversion over the lake, by which strong north winds blow warm surface water to the south, leaving the north shore much colder and with less oxygen. Some species of fish cannot adapt to this change, and "in many cases, they die." [However, it is becoming autumn in that region of the country, and thermal inversions are more rare at this time of the year. - Mod.TG]
Normally, the botulism bacteria Clostridium botulinum is found in sediments on the bottom of the lake. It becomes a toxic bacterium only when it is in an environment having no oxygen. The bacterium is generally dormant in a live fish, and forms a toxin once the fish is dead as part of the process of decomposition.
It's [the toxin] generally not found in live fish, and it has been very rare, until the last few years, that botulism has been found in birds which eat live fish, Cooper said. There were die-offs of thousands of birds which feed on live fish in the fall of 1998 and 1999 in the west end of Lake Erie and south end of Lake Huron, he said.
"That was when the question came up of how birds normally eating live fish are getting type E botulism. And we've now, in the last 2 years, had similar occurrences with dead fish and dead birds in the east end of Lake Erie."
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ProMED-mail
[One certainly hopes that this outbreak will remain confined to fish and birds. Type E botulism is well known to cause illness in humans, and is typically associated with the consumption of preserved or fermented fish, marine mammals, and beaver. Ethnic preparations of uneviscerated fish pickled in brine have also been associated with type E botulism in humans. Clostridium botulinum spores can be found in the intestinal contents of fish, which may explain why ungutted fish have been most often implicated in outbreaks of human disease.
The interested reader is directed to MMWR 41(29);521-522 Outbreak of Type E Botulism Associated with an Uneviscerated, Salt-Cured Fish Product -- New Jersey, 1992 and to MMWR 36(49);812-3 International Outbreak of Type E Botulism Associated With Ungutted, Salted Whitefish. - Man. Ed. DS]
http://lama.kcc.hawaii.edu/praise/news/eh171.html
